Here are some more basic fixes....

New front seat-belts and a swap of one of the back seat-belt latches, which was missing.  Now everything matches and is up to modern standards.  A rusted bolt on one of the front passenger belt took a torch and little convincing to come out, but it did finally relent.

Adjusted the tension on the passenger door lock so that it wouldn't lock without being pushed.   The 40 year-old pressure spring had lost some of its spring.  Deciphering how the mechanism actually worked took a bit.